The science of eggs – and why you’ve been buying the wrong ones

Stand in the supermarket for long enough and you’ll see it play out. Some shoppers automatically reach for the cheapest box they can find. Others gravitate towards premium brands with their farm shop-brown shells and deep orange yolks – eggs that seem to promise a better class of breakfast. Somewhere along the way, many of us came to believe that browner meant better: better welfare, better flavour, better nutrition.

The supermarket revealed this week that it will ditch brown eggs and only sell white-shell eggs under its own-brand label after research suggested they have a lower environmental impact. According to the retailer, white hens (which lay white eggs, who knew?) are smaller and “require less feed for the same egg output”, resulting in an “over 12 per cent reduction in carbon emissions compared to brown hens” – 12.7 per cent, to be suspiciously precise.

Sainsbury’s will no longer sell own-brand brown eggs on account of their environmental impact (PA)

The move has reignited a debate that many shoppers probably didn’t even realise existed. Why are some eggs white and others brown? Are brown eggs healthier? Do they taste better? And if British consumers have spent decades favouring brown eggs, have we been getting it wrong all along?

The short answer is yes. Much of what we think we know about eggs turns out to be little more than shell-deep.

Today, brown eggs dominate British supermarket shelves, but that wasn’t always the case. Until the 1970s, white eggs were commonplace in Britain. Then consumers began turning towards brown eggs amid growing perceptions that they were more natural and nutritious. According to the British Hen Welfare Trust, there was a widespread misconception that white eggs had been bleached, while brown eggs came to be associated with traditional farming and superior quality.

The association wasn’t entirely invented. White egg-laying hens were more commonly used in intensive farming systems because their smaller size meant more birds could be housed in the same space. Over time, consumers began treating shell colour as a proxy for welfare. Brown eggs came to signal a less industrial approach to farming, whether that was actually true of the individual egg in question or not.

14.5 billion

The shift was so dramatic that Britain eventually became an overwhelmingly brown-egg market – accounting for nearly 90 per cent of all eggs sold. Meanwhile, across the Atlantic, white eggs remained the norm: more than three-quarters of eggs sold in the US are white. For generations of Britons, white eggs became something you saw in American sitcoms rather than your local supermarket.

Over time, brown eggs acquired something else, too: status. Farm shops stocked them. Premium brands built entire identities around them. The darker the shell and orange the yolk, the more likely shoppers were to assume they were in for a middle-class breakfast.

The irony is that the premium we’ve been paying for brown eggs over the past 50 years hasn’t been buying us more nutrition, better flavour or higher welfare. We’ve been paying for bigger birds that eat more feed, lay fewer eggs and live shorter lives.

According to British Lion Eggs, “the colour of the egg shell depends on the breed of the hen”. Brown hens lay brown eggs and white hens lay white eggs… though this rule obviously doesn’t extend to blue eggs. Additionally, “There are no nutritional differences between brown or white eggs” and “while some consumers may believe that brown or white eggs taste better, there is no difference from a scientific perspective.”

That’s it.

White hens’ smaller size made them a favourite of intensive farming – and gave white eggs a reputation problem (Getty)

The shell colour doesn’t tell you how nutritious the egg is, how healthy the hen was or whether it will make a better omelette. For shoppers who have spent years buying Burford Browns on the assumption they were healthier or more flavoursome, that’s a rather embarrassing truth.

What shell colour can tell you, however, is a rough estimate of an egg’s environmental footprint – though even that comes with caveats. The colour itself isn’t what matters. What matters is the bird that laid it.

Sainsbury’s says research carried out with suppliers found that white eggs have a significantly lower carbon footprint than brown eggs because the hens that lay them are simply more efficient producers. White hens consume less feed while producing the same number of eggs, reducing the resources required across the supply chain.

Switching to white eggs can help “indirectly reduce demand on land and water used to grow feed crops”, the supermarket said. That matters because feed production accounts for 50-60 per cent of the environmental impact of egg farming.

Britain consumes around 14.5 billion eggs every year, producing an estimated 4.35 million tonnes of carbon dioxide emissions in the process. If the entire industry achieved the same 12.7 per cent reduction claimed by Sainsbury’s, emissions could fall by more than 550,000 tonnes of CO2 annually – roughly equivalent to removing nearly 300,000 cars from Britain’s roads.

Sainsbury’s says white hens not only consume less feed but also live longer and enjoy more productive laying lives. Environmentally, those are two distinct advantages.

12.7%

A longer lifespan means fewer replacement birds need to be reared. A more productive lifespan means more eggs are produced from the same resources. Together, both factors reduce the emissions attached to each individual egg.

Environmental credentials, however, are only one part of the story. A welfare-conscious shopper might reasonably wonder whether the same efficiencies that reduce emissions come at a cost to the birds themselves. Sainsbury’s argues the opposite. The retailer says white hens are generally more docile and less prone to feather pecking than their brown counterparts.

That may be true, but welfare experts caution against drawing conclusions from shell colour alone. The British Hen Welfare Trust says: “Whether an egg is brown, white or blue bears no real relevance on the living conditions of the hen that laid it.”

The code on the shell tells you far more than the colour of it (Getty/iStock)

Instead, shoppers concerned about animal welfare should focus on how eggs are produced. The most useful clue is not the colour of the shell but the code stamped on it. Organic eggs carry a 0, free-range eggs a 1, barn eggs a 2 and eggs from caged hens a 3 – though it’s worth noting that all major supermarkets no longer stock caged hen eggs.

That small number tells consumers far more than shell colour ever could. The same is true for flavour. Nowhere is this more evident than in the debate over which yolk is best.

The colour of a yolk is largely determined by pigments known as carotenoids, which occur naturally in things like maize, marigold, peppers and carrots. Feed hens a diet rich in these compounds and their yolks become darker and more orange. Similarly, feed a human enough carrots and they, too, will turn orange.

Some of those nutrients may be present in the final egg, but the benefits to humans are marginal. An orange yolk might indicate a hen that has spent more time outdoors, increasing the chances of foraging for carotenoid-rich plants and insects. Equally, it might simply reflect the season in which the egg was laid, with hens generally spending more time outside in spring and summer. More often, though, yolk colour is the result of a carefully controlled feeding programme. In other words, an orange yolk is frequently the consequence of a production decision made long before the egg reached your breakfast plate.

All of this to say, British shoppers have spent half a century falling for fake news about eggs. Brown shells don’t guarantee higher welfare. Orange yolks don’t guarantee better flavour. And neither tells you much about nutrition.

For something that inspires so much supermarket snobbery, the humble egg turns out to be surprisingly good at teaching a lesson: what looks better isn’t always better.

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